Female duck getting feisty.

I have 2 female ducks and 1 drake. My oldest female (phoebe) has become very aggressive in the past week or so. She is mounting my other female (louise) which I would assume is because of dominance but she is turning her tail like a drake. Phoebe is attacking my chickens when she has been with them her whole life and never has attacked them before. She loves when my Drake bites on her and chases him around but struts for louise. I'm very confused with her behavior. And today Phoebe has begun mounting my drake. What do I do to get her back to normal?